There is a need in the art to determine whether two devices that are communicating with one another are within a predetermined proximity of each other. This need may be based on a desire to ensure that two devices remain physically proximate, or based on a desire to enhance security by reducing the possibility of certain types of malicious attacks. With respect to the former, for example, one may want to ensure that an electronic monitoring device worn by a person on bail, or an electronic tracking device located on an automobile, remains within a predefined or predetermined distance of a monitoring station or monitoring terminal.
With respect to the latter scenario, while physical proximity of devices communicating with one another may enhance the security of the communication there is a need to ensure that the devices are actually proximate. For example, ultra-short range communication technologies (such as, for example, Near-Field Communication (NFC)) may be used in the process of establishing a secure communication channel between two devices. As one example, two devices with ultra-short range communication capabilities may be brought next to each other to exchange encryption keys for establishing a secure sockets layer (SSL) session. Due to the physical constraints of such ultra-short range communication methods, it is believed that the key exchange can only happen between devices that are physically located next to each other. However, various attacks still may pose serious security threats. For example, a relay attack (a variation of the man-in-the-middle attack) may be performed by using a fake terminal or hot spot equipped with signal re-transmitters to re-transmit the communication signal while the legitimate communication partner may be located far away.
Therefore, there is a need in the art for ensuring a communication partner at the other end of a communication link is within a predefined physical proximity.